Rendered bone contains varying amounts of fat or grease depending on the efficiency of the rendering process at removing tallow from the bone. Multiple sourcing of rendered bone results in a wide range of fat content in the starting bone material for gelatin manufacture. Fat contained in rendered bone is an impurity in photographic gelatin that must be removed during the gelatin manufacturing process. It is known that the fat content of bone directly effects photographic gelatin yield. Typically photographic gelatin yields are defined by the amount of gelatin produced with an absorbance at 420 nm of less than 0.150. Analysis of production data comparing low fat and high fat bone suppliers suggests that each 1% decrease in fat content of the starting bone results in a 0.4% increase in photographic gelatin yield.
Currently, fat or grease is removed at various stages throughout the gelatin manufacturing process with varying levels of efficiency. Typically, cattle bone used in the manufacture of high grade gelatin, is cleaned of its fats, grease, blood and bone marrow by hot water washing. The bone is then demineralized in a liquid/solid extraction/reaction process using an acid solution. Removal of minerals from the bone particles in the demineraliztion process yields particles of a material known as ossein. The gelatin is extracted from the ossein.
Following washing and acidulation, and sometimes liming of the cattle bone, the fat content ranges from 4-6% of the organic content of ossein. Although fat is reduced through each step of the gelatin manufacturing process, fat remaining in the final gelatin product is directly impacted by the fat content of the starting bone. Due to the inability to reproducibly reduce fat content of the bone to a low level, photographic gelatin yield is reduced. Ideally, to minimize photographic gelatin yield losses due to fat impurities a process for producing a uniform low fat rendered bone is required. This invention describes a single purification step specifically designed and optimized for fat removal from rendered bone.